* Barca banned from next two transfer windows
* Club guilty of breaking rules on signing minors
* Catalan club say will take its case to CAS (updates with Barca CAS appeal, details)
By Brian Homewood
ZURICH, Aug 20 (Reuters) - Barcelona have lost an appeal against a decision to ban them from the transfer market for two consecutive windows, soccer's world governing body FIFA said in a statement on Wednesday.
As a result, Barca, who were found guilty of breaching rules on the international transfer of under-18 players, will be banned from registering players during the next transfer window in January as well as the 2015 summer window, FIFA said.
FIFA also rejected Barcelona's appeal against a 450,000 Swiss francs (493,637 dollars) fine and have been given 90 days to regularise the situation of all the minor players concerned, the governing body said.
The ban was originally imposed in April and would have covered the current transfer window, followed by the next one in January.
However, Barcelona appealed later the same month and the ban was lifted pending the outcome of the disciplinary process.
The Catalan club, hugely proud of its Masia academy, said it would take the case to the Court of Arbitration for Sport (CAS).
"Barcelona cannot accept in any way a decision which attacks the sprit of our Masia, an example in human, sporting and academic development, recognised around the world," it said in a statement.
Since the ban was temporarily lifted, Barca have signed Uruguay forward Luis Suarez, Belgium centre back Thomas Vermaelen, France defender Jeremy Mathieu, Croatia midfielder Ivan Rakitic, Chile goalkeeper Claudio Bravo and Germany stopper Marc-Andre ter Stegen.
The first four players alone cost about $200 million.
"The FIFA Appeal Committee has decided to... confirm in their entirety the decisions rendered by the FIFA Disciplinary Committee in the respective cases relating to the protection of minors," said FIFA in a statement.
"FC Barcelona is to serve a transfer ban which will see the club prevented from registering any players at both national and international level for two complete and consecutive transfer periods, starting with the next registration period (January 2015)."
The Spanish Football Federation (RFEF) also lost its appeal against a 500,000 Swiss francs fine, FIFA said.
"The RFEF has been ordered to pay a fine of CHF 500,000 and granted a period of one year in which to regularise their regulatory framework and existing system concerning the international transfer of minors in football."
FIFA, which did not give any further details of which rules had been broken or which players were involved, allows the international transfer of under-18 players in only rare circumstances.
They are permitted if the player's parents move to the club's country for reasons not linked to football or if the transfer takes place within the territory of the European Union or European Economic Area, and the player is between 16 and 18.
The former rule has led to concerns that rich clubs could arrange for the player's parents to move to their country, and get jobs, behind the scenes.
In the latter case, clubs must ensure that the player is given a full education or training that would allow him to pursue a career outside football, as well as football training "in line with the highest national standards."
In addition, the player must not be younger than 16.
Clubs who run academies must report all minors who attend to their own national association, who in turn must keep a register including names and dates of birth.
The rules also state that "through the act of reporting, academies and players undertake to practise football in accordance with the FIFA Statutes, and to respect and promote the ethical principles of organised football."
(1 US dollar = 0.9116 Swiss franc)
($1 = 0.7530 Euros)
($1 = 0.6012 British Pounds) (Writing by Brian Homewood in Berne; editing by Ken Ferris)